It is known in the art to use air flow in a paint booth to control the flow of the excess paint, be it liquid drops or powder particulate, which is discharged from the paint source, such as an atomizer or paint or spray gun, etc., and not actually applied to the articles being painted. It is also known to attempt to control the velocity of the air flow in the booth and/or to try to keep the air flow velocity constant to provide a consistent environment for painting. For example, U.S. Pat. No. 5,095,811 teaches measuring the air flow velocity in a powder paint booth and adjusting the incoming air volume to keep the velocity constant in order to compensate for the fact that the articles being painted are moving through the booth and otherwise would have altered the air flow velocity. The actual velocity adjustment in that patent is taught as being accomplished by sensing the air speed and then through a controller adjusting the speed of the air feed and/or air exhaust fans or blowers.
A prior art technique for sensing such paint or powder booth air velocity was by pitot tube. However, over a period of time the narrow pitot tube tended to clog, was not accurate when dirty, and its sensitivity changed and effect the booth's operation.
In a previous wind chill measuring device, a pendulum moving along a scale was used to determine air speed by taking visual readings off a scale. See U.S. Pat. No. 4,091,667.
In powder booths the excess powder not applied to the articles being painted is in the form of airborne particulate, is recovered and collected on the surfaces of cartridge filters. The air is exhausted from the booth and is pulled through the filters to be treated and recirculated or discharged. In other types of dust booths where an airborne particulate is generated, such is by painting, grinding, sanding, or the other repair or work, the particulate is similarly collected or recovered. The powder or particulate as it is collected tends to build up on the filters. Periodically, in order to extend the time between a filter's installation and the time it must be replaced, the filter is pulsed, with some form of vibration, usually in the form of an air blast or "shot" or pulse of compressed air. For example, see U.S. Pat. Nos. 4,770,118 or 4,913,085, which teach in column 8 thereof, that the "pulse duration and intervals can be determined to be different from normal operation values. These factors can also be varied periodically, by self action, which can be accomplished without further ado through an electronic control."